A quick engineering reference for electrical & mechanical project work — wiring colour codes, common formulas, units and the standards we design and build to. Figures below are indicative and must always be verified against the applicable standard and manufacturer data for the actual installation.
1. Electrical Wiring Colour Codes
Single-phase fixed wiring conductor identification.
| Conductor | IEC / BS 7671 (2006 onward) | Old UK (pre-2006) | USA (NEC) |
|---|---|---|---|
| Line (Live) | Brown | Red | Black |
| Neutral | Blue | Black | White |
| Protective Earth (PE) | Green / Yellow | Green / Yellow | Green (or bare) |
2. Three-Phase Colour Codes
| Conductor | IEC (current) | Old UK | USA (120/208V) |
|---|---|---|---|
| Line 1 (L1) | Brown | Red | Black |
| Line 2 (L2) | Black | Yellow | Red |
| Line 3 (L3) | Grey | Blue | Blue |
| Neutral (N) | Blue | Black | White |
| Earth (PE) | Green / Yellow | Green / Yellow | Green |
3. Common Electrical Formulas
| Quantity | Formula |
|---|---|
| Ohm's Law | V = I × R |
| Power (DC / single-phase) | P = V × I × cosφ |
| Power (three-phase) | P = √3 × VL × IL × cosφ |
| Apparent power | S = √3 × VL × IL (VA) |
| Power factor | cosφ = P / S |
| Voltage drop (single-phase) | Vd = 2 × I × L × R / 1000 |
| Efficiency | η = (Pout / Pin) × 100% |
4. SI Prefixes
| Prefix | Symbol | Factor |
|---|---|---|
| Giga | G | 109 |
| Mega | M | 106 |
| Kilo | k | 103 |
| Milli | m | 10-3 |
| Micro | µ | 10-6 |
5. Common Unit Conversions
- 1 kW = 1.341 HP · 1 HP = 0.746 kW
- 1 bar = 100 kPa = 14.5 psi
- 1 inch = 25.4 mm · 1 foot = 0.3048 m
- 1 kWh = 3.6 MJ
- °C = (°F − 32) × 5/9
6. Cable Selection — Derating Factors
Current-carrying capacity from the base rating must be corrected for site conditions before final selection:
- Ambient temperature — apply the temperature correction factor for the installation environment.
- Grouping — apply the grouping factor where cables are bunched or run together.
- Installation method — buried, in conduit, on tray, or clipped direct each carry a different rating.
- Thermal insulation — cables in or surrounded by insulation are further derated.
Detailed ampacity tables must be taken from IEC 60364-5-52 (or the local equivalent) together with the manufacturer's data sheet.
7. Referenced Standards
- IEC 60364 — Low-voltage electrical installations
- IEC 60227 / 60228 — Conductors of insulated cables
- IEC 60364-5-52 — Selection & erection of wiring systems (current-carrying capacity)
- BS 7671 — Requirements for electrical installations (IET Wiring Regulations)
- NFPA 70 (NEC) — National Electrical Code
- IS 732 / IS 3043 — Code of practice for electrical wiring & earthing
This page is maintained by EPC Services and is provided for general guidance only.